A thermal printhead typically comprises a row of closely spaced resistive heat generating elements which are selectively energized to record data in text, bar code or pictorial form. In operation, the thermal printhead heating elements selectively receive energy from a power supply through central circuits in response to stored data information. The heat from each energized element may then be applied directly to thermally sensitive material or to a dye coated web to effect transfer of the dye to paper or other designated receiver material.
In one type of thermal printhead which is capable of printing colored images, a donor containing a repeating series of spaced frames of different-colored, heat-transferrable dyes is employed. The donor is disposed between a receiver, such as coated paper, and a printhead formed of a plurality of individual resistive heat generating elements. When a specific resistive element is energized, it produces heat and causes dye from the donor to transfer to the receiver.
These thermal dye transfer printers offer the advantage of a true continuous tone dye density transfer. This result is obtained by varying the energy applied to each heating element, thereby yielding a variable dye density image pixel in the receiver. An effective means for attaining this end involves the use of a laser as the thermal source to heat a donor containing the material to be transferred to a receiver.
Heretofore, it has been common practice to employ a donor including a heat absorbing layer, a base layer and a dye layer which includes a binder and a dye. The heat absorbing layer employed for this purpose contains light absorbing materials such as carbon black or an infrared dye. Unfortunately, such prior art techniques have not proven to be completely satisfactory. More specifically, studies have revealed that the use of carbon black as the light absorbing material limits the ability to heat uniformly and often results in small particle transfer and color contamination. Similar difficulties with respect to color contamination have been encountered with infrared dyes.